1. Field of the Invention
The invention relates to a method for treating a product in the form of a foodstuff or a pharmaceutical. The method detects leaks in a package, particularly in a food and pharmaceutical package and increases the shelf life of the quality of the foodstuff and pharmaceutical by determining the integrity and tightness of the package nondestructively. The invention also relates to a device for detecting a leak in a food or pharmaceutical package, containing a product in the form of a foodstuff or a pharmaceutical.
2. Description of Related Art
It is known to treat foodstuffs by preserving them in substantially oxygen-free packages to reduce the aging effect of oxygen on the product. The integrity of the package is important to guarantee the freshness and safety of a product in the package, such as a foodstuff, for a specified period of time. For that purpose, foodstuffs are often packed in airtight, airless packages. The packing material may vary. Various soft and semi-hard plastic packages and wax and plastic coated cardboard packages are generally used. The packages may also be hard, typically glass and metal packages. If there is a hole in the package and it leaks, the contents of The package spoil in a considerably shorter time than the projected shelf life of The product. Depending on the contents of the package, the spoilage may appear as too high of a bacterial content, a taste defect, an odor defect, a color defect, or a viscosity defect The size of a permissible hole varies depending on the contents, the storage conditions and the required shelf life of the package. Holes larger than about 20-30 .mu.m should normally not be permitted in packages. Holes having a size below 10 .mu.m usually do not present any problems.
A conventional nondestructive method for testing the integrity of a package is to place the package in a vacuum chamber. If the vacuum changes, the package is determined to be defective. Another way is to immerse the package in liquid and to monitor whether bubbles are formed in the water; if so, the package leaks.
All of the above methods can be used, but have the problem of being too slow. They are only suitable in spot tests for testing package tightness in production plants. Hence, it is not possible to maintain a sufficient production rate in production plant if every package was tested by the above methods.
To provide faster testing methods it is known to add gas to a package, to place the package in a chamber which has been evacuated of air and/or whose pressure is lower than that of the package, and to measure the gas leaking from the package into the chamber. U.S. Pat. No. 5,029,463 discloses such a method for detecting a leak in a package. The purpose of the method is to operate at the same speed as the packaging line. It has been contemplated to use helium as a test gas. Since helium is an inert gas, it can be used safely in conjunction with many materials. The example in the publication teaches that the testing time is 30 seconds when the test gas contains helium. 1-5% by volume is recommended as the concentration of helium in the tracer gas, the remainder being carbon dioxide or nitrogen. The publication states that gases other than helium, such as CO.sub.2, N.sub.2 O, CH.sub.4, can be used as a test gas. The drawback of the method of U.S. Pat. No. 5,029,463 is that it is too slow to be used in conventional fast production plants. Furthermore, this method requires creating a relatively deep negative pressure in the chamber in order to achieve an adequately short dwell time for measuring. Creating a deep negative pressure is time-consuming and requires expensive equipment. The time for creating the required negative pressure and the testing time are not sufficiently short to allow the method to be implemented in a fast production plant for testing every package. The drawbacks of helium also include the fact that normal air contains helium which must be removed from the measuring chamber in order for the helium in the air not to interfere with the measurement, which further slows down the method. Alternatively, the helium content of the test gas added into the package must be high, which makes the method expensive. U.S. Pat. No. 5,029,463 also discloses an apparatus for detecting a leak in a package. Since the device is based on the method in which helium has been recommended for use as a test gas, the apparatus comprises a plate within a test chamber, adapted to springedly press the package when the package is in the chamber. The shape of the plate is selected in accordance with the shape of the package. The plate makes the apparatus complicated.
U.S. Pat. No. 5,386,717 discloses a method for detecting a leak in a package. In accordance with the method, helium is used as a probe gas. 1.3-13 mbar (1 torr-10 torr) is recommended as the pressure for the test chamber. Creating such a negative pressure is expensive and time-consuming. Helium has the drawbacks set out above. Since air naturally contains helium (about 5 ppm) which may interfere with the test results, in accordance with the publication, the chamber must be purged. The purging gas must not contain any probe gas. Since air cannot be the purging gas, gases must be used as purging gases that make the method expensive to implement. As the purging gas is removed from the chamber in connection with each test period, a new purging gas must be supplied before the next test. In the publication, hydrogen gas is not believed to be suitable for use as a probe gas, as hydrogen is thought to cause measurement errors when a negative pressure is generated in the test chamber. The publication also discloses an apparatus for carrying out the method. In accordance with the above, the apparatus comprises an expensive vacuum means and means for flushing the test chamber with a purging gas.
U.S. Pat. No. 5,499,529 discloses a method for detecting a leak in a package. In accordance with the method, a tracer gas heavier than helium, preferably SF.sub.6 or CF.sub.4, is used. The gas is selected so as not to diffuse from the package outwardly through the packing material. A drawback of helium that has been mentioned, for example, is the fact that it may diffuse through plastic film, rubber, paper etc., which are generally used for packages.